IL-8 and IL-6 mRNA half-life after exposure to TNF-α. Equal cell numbers from clones, indicated on the x-axis, were stimulated with 5 ng/ml TNF-α for one hour before 5 μg/ml Actinomycin D (ActD) was added to block further transcription. At 0, 40 and 80 min after ActD addition, total RNA was extracted with TriZol. RNA was dot blotted and hybridized with 32P-labelled IL-8, IL-6 and GAPDH probes. Signals were quantified on a phosphorimager and IL-8 and IL-6 mRNA levels were normalized for variable loading using GAPDH mRNA levels. Half-life of the mRNA in the clones was calculated using linear regression. Data represent the mean ± SEM from 2 independent experiments (triplicate samples).